1. Field of the Invention
This invention relates to the preparation of copolyamides and is particularly concerned with aromatic-aliphatic copolyamides.
2. Description of the Prior Art
Various types of polyamide polymers are known to those skilled in the art, see for example The Encyclopedia of Polymer Science and Technology, Vol. 10, pp. 347-593, 1969, Interscience Publishers, New York, N.Y. The various kinds of repeating units disclosed therein which are linked by the carbonamide group ##STR2## determine the variation in physical properties observed for the different types of polyamides. Physical properties like melting point and solubility are almost solely dependent on the type of repeating unit employed. For example, when all the repeating units are aromatic the polyamide has such a high melting point that melt processability, such as injection molding, is precluded because polymer decomposition begins to occur before the melt stage is ever reached.
Alternatively, when the repeating units are mixed aliphatic-aromatic, as in the case of a polyamide prepared from an aliphatic dicarboxylic acid and an aromatic diamine, the polymer is injection-moldable but, because of high crystallinity, is brittle, opaque, and possessed of low elongation. In fact, when the dicarboxylic acid component is the residue of either adipic, pimelic, or suberic acid and the aromatic diamine is 4,4'-methylenedianitine, the corresponding polyamides have decomposition temperatures below their melting points. This behaviour precludes melt processing these polymers; see J. Polymer Sci. lO, Part A-1, 1547, 1972. Finally, when the repeating units are all aliphatic as in nylon-6,6, the polymer is injection moldable but is limited by the end-use temperature to which it can be exposed.
The prior art discloses methods for the preparation of copolyamides derived from the reaction of mixtures of aliphatic dicarboxylic acids and aromatic diamines, or aromatic diisocyanates in either catalyzed melt condensation, solvent-interfacial condensation, or polar solvent condensation, as set forth in U.S. Pat. Nos. 3,408,334, 3,640,970, and 3,642,715, respectively. Also U.S. Pat. No. 3,651,022 discloses a method for the formation of linear polyamides which are useful for the melt spinning of fibers by reacting 4,4'-methylenedianiline (MDA) with a 1.01 to 1.09 molar excess of a C.sub.9 -C.sub.12 aliphatic dicarboxylic acid or mixtures of such acids.
Further, the art teaches that when amorphous, clear, tough moldable polyamides are desired which possess good physical properties, and do not crystallize, then the expensive reduced form of MDA, and its derivatives are to be used. Generally speaking this involves the formation of polyamides from either bis(4-aminocyclohexyl)methane (PACM), or 2,2-bis(4-aminocyclohexyl)propane (PACP) and aliphatic dicarboxylic acids including mixtures thereof; see U.S. Pat. Nos. 2,512,606, 3,703,595, 3,840,501, and 3,842,045.
The prior art does not disclose a polyamide composition which is easily heat processed, for example by molding, extruding, etc., and is amorphous when extruded or worked under one temperature range, or crystalline when extruded or worked under a higher temperature range, and at the same time characterized by good physical properties and higher end-use temperatures as compared with known aliphatic polyamides, and, furthermore, which is easily prepared from readily available and inexpensive starting materials.
The copolyamides prepared in accordance with the present invention meet the above requirements and are set forth in detail hereinbelow.